1. Field of the Invention
The present invention relates generally to electrical contact constructions and, more particularly, to electrical contact constructions for cordless telephone handset apparatus.
2. Background of the Invention
FIG. 1 is a schematic diagram showing a known cordless telephone. Conventional cordless telephone 10 includes base unit 11 and handset 12. The left half of FIG. 1 shows base unit 11 without handset 12 placed within it. The right half of FIG. 1 shows handset 12 rested within base unit 11.
Base unit 10 includes battery charging equipment 19 and a cradle cavity that is configured to receive handset 12. The cradle cavity has electrical contacts 13 that are suitably disposed within the cradle cavity, so that upon placement of handset 12 in the cradle cavity, electrical contacts 13 physically come into contact with corresponding electrical contacts 14 of handset 12. Battery charging equipment 19 in base unit 11 (and possibly, in handset 12) is then activated to supply current to the battery in handset 12 to recharging the battery.
In many such handset constructions, electrical contacts 14 in the bottom portion of handset 12 are continuously coupled electrically with the internal electrical circuitry (not shown) of handset 12. Because of this construction, it is often possible that during the use of handset 12, the operator, and, in turn, handset 12, may acquire a substantial static electrical charge. During the act of placing handset 12 into the cradle cavity of base unit 11, a substantial electrostatic discharge (ESD) may occur due to the static energy that is discharged from handset 12 and/or the operator, into base unit 11. The discharge may result in damage to the circuitry in either or both of handset 12 and base unit 11.
Accordingly, known cordless telephone constructions have typically required the presence of special circuitry within base unit 11 to dissipate or otherwise address the electrical energy of a discharge to protect the functional circuitry of telephone 10. Such protective circuitry or other structures (mechanical and/or electrical) often significantly add to the complexity and cost, as well as the physical size, of the telephone components.
In addition, the charging contacts in base unit 11 of handset 12 need to have a spring-action interface between contacts 13 of base unit 11 and electrical contacts 14 of handset 12. The spring-action interface enables contacts 13 to be kept in continuous contact with handset contacts 14. The spring-action interface also permits contacts 13 themselves to be moved to address the clearance between the cradle cavity of base unit 11 and handset 12.
Contacts 13 apply a spring force exerted by thin sheet of metal 15. Thin sheet of metal 15 can be, for example, about 0.15 mm thick. Preferably, thin sheet of metal 15 is made of a phosphorous bronze, nickel-plated sheet. Thin sheet of metal 15 supports contacts 13 at one end and is connected to the interior of base unit 11 at the other end. Metal sheet 15 provides for an elastic reciprocal travel within a controlled travel stroke. Metal sheet 15 may well be durable enough for the service life of telephone 10. Nevertheless, there may exist non-uniformities in the spring force of individual charge contacts due to various fabrication and quality control issues.
Such thin sheet metal construction for known resilient contact support structures leads to a relatively non-robust element. Handling during manual fabrication processes may compound irregularities in initial deformation. In addition, such thin sheet metal elements may complicate the assembly process, increasing the assembly time and assembly costs.
Such thin sheet metal contact supports are typically attached to base unit 11 by screw fasteners 16 (see FIG. 2), which may exert forces on metal sheet 15 that may skew the alignment of charge contacts 13 within its chassis aperture, such that contacts 13 may require adjustment on a potentially individualized basis (see left half of FIG. 2). Such known contacts are also susceptible to misalignment due to operator misuse, or attempts to clean the charge contacts with a pen (see right half of FIG. 2).
A typical known electrical contact construction incorporates metal contact head 18 that is a protrusion that leans through opening 17 in base unit 11. This construction requires clearance between contact head 18 and the chassis to prevent contact head 18 from being stuck because of frictional force, in case contact head 18 rubs against the base chassis. The light spring force available in thin sheet metal 15 may not be adequate to ensure that in the event of such frictional contact between contact head 18 and the chassis, contact head 18 will be reliably pushed back up through aperture 17 in the chassis, to the specified position. To avoid imposition of such frictional forces, a visible gap may be created that may permit the penetration of liquid, dust, etc. Such a gap may become even more pronounced if/when the electrical contact becomes misaligned. Damage and premature degradation of base unit 11 may be a result.
In addition, a contact for a base unit for a cordless telephone should be robust enough to resist and withstand a certain amount of possible abuse by the owner.
Accordingly, there is a need for an electrical contact construction that may be employed in the environment of a cordless telephone handset and a base unit, as well as in other environments, in which the electrical contacts have an improved design that provides a degree of protection against damage through the propagation of a static electrical discharge.
Furthermore, it would also be desirable to provide an electrical contact construction that is provided with a robust design to provide for a reliable operation over an expected life cycle of the telephone.
Moreover, it would be desirable to provide an electrical contact construction that has an advantageous ease of assembly.
These and other desirable characteristics of the invention will become apparent in light of the present specification and drawings.